1. Technical Field
The present invention relates to methods of growing gallium nitride crystal, to gallium nitride crystal substrates, to methods of manufacturing epi-wafers, and to epi-wafers.
2. Description of the Related Art
Gallium nitride (GaN) crystal is employed as substrates for light emitting diodes (LEDs), laser diodes (LDs), and like semiconductor devices. With gallium nitride crystal, which has an energy bandgap of 3.4 eV and high thermal conductivity, because an electrode can be provided on the crystal back side, the driving (operating) voltage of the semiconductor devices can be reduced.
Examples of methods of manufacturing such semiconductor devices include the following method set forth in Japanese Unexamined Pat. App. Pub. No. 2005-251961 (Patent Document 1). First, a seed-crystal layer composed of Group III-nitride crystal is deposited onto a first principal face of an undersubstrate by a deposition technique such as metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). After that, III-nitride single crystal is grown onto the seed crystal by a liquid-phase growth technique and the undersubstrate is removed, whereby a III-nitride single crystal wafer is manufactured. Next, semiconductor devices are formed onto a first principal face of the III-nitride single crystal wafer. Then, with an objective such as improving the device's heat dissipation characteristics, the second principal face of the III-nitride single crystal wafer is subjected to a removing process by means of grinding, polishing, etc. to reduce the wafer thickness.
Furthermore, in Japanese Unexamined Pat. App. Pub. No. H11-68156 (Patent Document 2), for example, depositing a III-nitride semiconductor layer onto a substrate by MOCVD is disclosed. Patent Document 2 describes that in this growth, disilane (Si2H6) is employed, with as its carrier gas a refined hydrogen gas whose dew point has been brought to −90° C., to grow a 0.2 μm-thick n-type GaN layer doped with silicon (Si).
However, a problem with, as in Patent Document 1, performing a process for thickness reduction on the second principal face of III-nitride single crystal wafers has been that cracking occurs, with impurities incorporated into the crystal during growth being a causative factor.
Furthermore, in Patent Document 2, each layer is grown by MOCVD, which has been prohibitive of making the thickness of the deposited layers greater.